Ammeter reading high

K

KiwiRover

Active Member
Did a bit of work on the '72 V8 today. I have just installed an electronic ignition kit from Simon BBC and coupled it with a Bosch GT40 non-ballasted coil. I bypassed the ballast wire by running a new cable from the back of the tacho through to the coil. Everything went smoothly and according to plan and the car runs well and sounds healthy, however I noticed that on the drive home, the ammeter is now reading +30 (ish) constantly. I'm pretty sure it wasn't doing that before but I'm not sure what has happened. Does the ignition and higher output coil draw that much more current or has something gone horribly wrong?
Any suggestion or advice greatfully received! :?
 
does disconnecting the tacho wire from the coil sort it?

Guessing that it's just in the wrong place in the circuit. I dont know the specifics of where it goes, but it must be something of this nature...

Rich
 
does disconnecting the tacho wire from the coil sort it?
Click to expand...

Yes. The engine stops! :LOL:


Seriously though, power is supplied from the fuse box to the tacho, then from the tacho straight to the coil via a resistance wire. All I have done is bypass the resistance wire. Not sure why that should have made any difference. There is no direct relationship between the tacho circuit and the ammeter and turning on the lights, heater, wipers etc has the usual effect: the needle flickers slightly but stays level, it's just doing it with a seriously positive reading. :shock:
 
Hmm, drove in to work this morning, running fine, ammeter at +30. Turned the car off, then when I restarted it 5 minutes later the tacho died :x Car still runs fine though. I guess I'll put the ballast wire back in and take a live coil feed from somewhere else and see if that works.
 
Had a bit more of a play. I swapped the tacho and refitted the original ballast wire and coil. Worked fine, tacho working, ammeter +30.
Hooked up a 12v supply to the coil, tacho stopped. I noticed that the ammeter sits a little high when turned off so I swapped this too. It now reads about +10 when running which is better but I have no idea if either of them are accurate. I decided to heed the dire warnings on Simon BBC's website about ballasted coils and reconnected it all back up the way I set it up yesterday with the bypassed ballast and 12v coil. I guess I'll see if the tacho dies again. :?
 
It sounds as if you have a wrong wire connected somewhere.
A word of warning, do not trust the factory wiring diagram!
depending on what Tacho you have fitted the current for the coil does not go thru it but merely senses the voltage waveform from the switch side of the coil.
As far a I know from my P6B (oct 74 build) the Ammeter rarely reads any thing when running, only deflecting when headlights and such are running.

My advice is take the instrment panel off and trace the wires and loom to see if they A: follow you wiring diagram and B: go where they should.

PS discovered when putting the Pertronix unit (running unballasted) that the wiring diagram did not agree with factory reality, my car is un-muddified from factory :)

Graeme
 
Could be a bad earth maybe - would explain current trying get to earth whatever way possible?

Just checked the wiring diagram i have ( haynes book of lies of course ) and it appears that if the ballast resistor was taken out and not replaced with at least a straight through wire it could shove current through the ammeter.

Rich.
 
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